Micron-size polymer particles and inorganic particles are used as fillers and specimens in a variety of fields, such as electrical and electronic materials, optical materials, paints, inks, construction materials, biological and pharmaceutical materials, and cosmetics. In recent years, active research has been carried out particularly on particles of unusual, non-spherical shapes. Because such particles confer diverse properties, including optical characteristics and tactile feel, new applications are constantly being developed.
The inventors have been working on the development of elliptical or needle-shaped polymer particles of high aspect ratio, and have discovered particles with characteristics superior to those of conventional spherical particles in terms of such properties as hiding power, light-diffusing ability and tactile qualities (Patent Documents 1 and 2).
However, although elliptical or needle-shaped polymer particles do have excellent characteristics owing to their shape, control of the shape and particle size tends to lead to an increase in impurities and agglomerates, which sometimes complicates filtration and classification and is thus a major problem.
In light of such circumstances, from an industrial standpoint, there has existed a desire for a method of producing polymer particles which is able to precisely and stably obtain such shapes.